1. Field of the Invention
The present invention relates to a user interface and method for dynamic range adjustment for an image capturing device.
2. Description of the Related Art
Dynamic range is typically defined as the ratio between the maximum and minimum values of physical measurement. In the world of photography and image processing, dynamic range is the ratio of saturation to noise. More specifically, the ratio of the intensity that just saturates the camera to the intensity that just moves the camera response one standard deviation above camera noise. And, even more specifically, dynamic range represents the ratio of two luminance values.
The human visual system has a relatively large dynamic range. For example, human vision can typically see objects in starlight or in bright sunlight and can adjust relatively well to scenes with very dark and bright areas. Typical photo-detectors on the other hand have a much more limited range of luminance data that they can capture. The linear response of these sensors imposes an abrupt limit to the dynamic range captured once the sensor capacity has been reached.
Digital images that have shadows and highlights and are captured using these photo-detectors require exposure adjustment of either the shadows, highlights, or both. This can lead to improper exposure of areas of the image, which can result in a poor level of detail in those areas due to excessive noise level or saturation.
This is why you cannot get what the human eye is seeing when capturing a high dynamic range scene with a standard camera. If you capture details in the shadows due to long exposure times, blown-out highlights result. Conversely, details in the highlights can be captured with short exposure times, but then contrast in the shadows is lost.
Currently, there is a trend in the area of digital photography to try and increase the current limitations of dynamic range. One approach has been to develop high dynamic range imaging sensors. However, these sensors have mainly been developed for the military, security, and other similar applications, and have yet to make their way into mainstream consumer level digital cameras. The majority of consumer level digital cameras still rely on conventional CMOS and CCD imaging sensors, which have limited dynamic range.
Photographers have been relying on multiple imaging capture to increase the dynamic range of digital photographs captured with such cameras. In this method, differently exposed photographs of the same scene are merged into an image with details in both highlights and shadows. This is known as exposure bracketing or blending. The exposure bracketing consists not on uniform steps of exposure but exposures corresponding to the exposures calculated based on brightness histogram adjustments by the user. This is accomplished using various commercially available post-processing software applications.
Once the high-dynamic image is captured there is the additional problem of the fact that most displays are unable to display high-dynamic range images. Therefore, the captured high-dynamic range image has to be processed, in a method known as tone mapping, the tonal range of a high dynamic range image of a scene is compressed in order to obtain its details in highlights and shadows. The initial image is either generated from differently exposed photos or obtained using a high dynamic range camera, as previously discussed.
In light of the above, what is needed is a method for easily specifying automatic exposure(s) based on manual user region selections and degree of visibility desirable for each region on commonly available digital cameras at the time an image is captured.